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ABOUT THIS IMAGE:

The object shown in these NASA/ESA Hubble Space Telescope images is a
remarkable example of a star going through death throes just as it
dramatically transforms itself from a normal red giant star into a
planetary nebula. This process happens so quickly that such objects are
quite rare, even though astronomers believe that most stars like the Sun
will eventually go through such a phase.

This star, with the prosaic name of OH231.8+4.2, is seen in these
infrared pictures blowing out gas and dust in two opposite directions.
So much dust has been cast off and now surrounds the star that it cannot
be seen directly, only its starlight that is reflected off the dust. The
flow of gas is very fast, with a velocity up to 450,000 mph (700,000
km/h). With extreme clarity, these Hubble Near Infrared Camera and
Multi-Object Spectrometer (NICMOS) images reveal that the fast-moving
gas and dust are being collimated into several thin streamers (on the
right) and a jet-like structure (on the left), which can be seen
extending away from the centers of both pictures. On the right, wisps of
material in jet-like streamers appear to strike some dense blobs of gas.
This interaction must produce strong shock waves in the gas.

The pictures represent two views of the object. The color image is a
composite of four images taken with different NICMOS infrared filters on
March 28, 1998. It shows that the physical properties of the material,
both composition and temperature, vary significantly throughout the
outflowing material. The black-and-white image was taken with one NICMOS
infrared filter. That image is able to show more clearly the faint
detail and structure in the nebula than can be achieved with the color
composites.

Observations by radio astronomers have found many unusual molecules in
the gas around this star, including many containing sulfur, such as
hydrogen sulfide and sulfur dioxide. These sulfur compounds are believed
to be produced in the shock waves passing through the gas. Because of
the large amount of sulfur compounds, this object has earned the
nickname "The Rotten Egg" Nebula. It resides in the constellation
Puppis.

These NICMOS data pose a serious challenge to astrophysical theorists:
How can a star generate such tightly collimated streams of gas and dust
and accelerate them to such very high velocities? William B. Latter from
the California Institute of Technology and his group are using these
data to obtain a better understanding of the detailed structure in the
outflowing material, look for evidence for the origin of the thin
streamers and jets, and learn more about the star itself. This
information will give astronomers a more complete understanding of the
final stages in the lives of stars like our Sun.

These results were presented at a conference called "Asymmetrical
Planetary Nebulae II: From Origins to Microstructures," Aug. 3 to 6,
1999 at the Massachusetts Institute of Technology. The results also will
be published in the Astrophysical Journal.